U.S. patent number 4,915,585 [Application Number 07/343,305] was granted by the patent office on 1990-04-10 for rotary-wing aircraft rotor head having resilient-return interblade ties with built-in damping.
This patent grant is currently assigned to Aerospatiale Societe National Industrielle. Invention is credited to Bruno Guimbal.
United States Patent |
4,915,585 |
Guimbal |
April 10, 1990 |
Rotary-wing aircraft rotor head having resilient-return interblade
ties with built-in damping
Abstract
The invention relates to a rotor head having interblade ties
with resilient return in lag and with built-in damping, wherein
each tie is connected, to each of the two rotor blades joined by
it, by articulation means comprising a main ball retained on a
member connecting a blade to the hub and centered on or in
immediate proximity to the pitch change axis of the corresponding
blade. A single main ball may be connected to the adjacent ends of
two neighboring ties by a connection member having the shape of a V
open towards the hub, or else each tie is connected to a connection
member by a respective one of two main balls offset transversely in
relation to the pitch change axis of the blade and/or radially
along said axis. Application to the main and/or auxiliary rotors of
helicopters.
Inventors: |
Guimbal; Bruno
(Chateauneuf-les-Martigues, FR) |
Assignee: |
Aerospatiale Societe National
Industrielle (Paris, FR)
|
Family
ID: |
9365866 |
Appl.
No.: |
07/343,305 |
Filed: |
April 26, 1989 |
Foreign Application Priority Data
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Apr 29, 1988 [FR] |
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88 05816 |
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Current U.S.
Class: |
416/140; 416/107;
416/141 |
Current CPC
Class: |
B64C
27/51 (20130101) |
Current International
Class: |
B64C
27/00 (20060101); B64C 27/51 (20060101); B64C
027/38 () |
Field of
Search: |
;416/14A,141A,138A,14R,141R,106,107 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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3148903A1 |
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Jun 1983 |
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DE |
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1442684 |
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May 1966 |
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FR |
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1465027 |
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Jan 1967 |
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FR |
|
1465027 |
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Jan 1967 |
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FR |
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2125150 |
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Sep 1972 |
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FR |
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2486492 |
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Mar 1978 |
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FR |
|
2584995 |
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Feb 1987 |
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FR |
|
602994 |
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Jun 1948 |
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GB |
|
643474 |
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Sep 1950 |
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GB |
|
654757 |
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Jun 1951 |
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GB |
|
Primary Examiner: Powell, Jr.; Everette A.
Attorney, Agent or Firm: Armstrong, Nikaido, Marmelstein,
Kubovcik and Murray
Claims
I claim:
1. A rotary-wing aircraft rotor head, of the type comprising a hub
to which each blade of the rotor is held by a connection member
fixed to the blade and connected to the hub with the aid of
articulation means permitting angular oscillations of the blade
about a single point on which the flapping axis, the lag axis and
the longitudinal pitch change axis of the blade are convergent, the
rotor head also comprising an interblade connection device
consisting of elongated resilient-return ties with built-in
damping, the number of which ties is equal to that of the blades
and which are mounted substantially in a ring around the hub, so
that each of them connects together two neighboring blades of the
rotor, each tie comprising at least two rigid elongated members,
each of which is provided with means for the articulated connection
of a respective end of the tie to a respective one of the two
blades connected by said tie, and which are connected to one
another by at least one resilient return member of the two rigid
members, for return to a relative initial position, and by at least
one member damping all relative movement of the two rigid members,
at least in the longitudinal direction of the tie, wherein said
means for the articulated connection of each tie to a blade
comprise a main ball whose center is situated on or in immediate
proximity to the longitudinal pitch axis of the blade and which is
retained, on the means connecting the blade to the hub, radially on
the outside, relative to the center of the hub, of the point of
intersection of the lag, flapping and pitch change axes, which
point constitutes the single center of articulation of the
connection means on the hub.
2. A rotor head as claimed in claim 1, wherein said means
articulating the connection member of a blade on the hub comprise a
thrust bearing articulation of the laminated spherical type
constituting at one and the same time the member retaining the
blade against centrifugal force and a flapping articulation, a lag
articulation, and a pitch articulation, with its center at the
intersection of the flapping, lag and pitch axes of the
corresponding blade.
3. A rotor head as claimed in claim 1 wherein the means for the
articulated connection of two neighboring ties on one and the same
blade comprise a single main ball whose center is situated on the
pitch change axis of the blade.
4. A rotor head as claimed in claim 3, wherein said single main
ball is connected to the adjacent ends of two neighboring ties by a
rigid connection member comprising two arms radially inclined
towards the hub and disposed laterally one on one side and the
other on the other side of the pitch change axis of the blade, the
two arms being attached to one another by a ball eye surrounding
the main ball, and the free end of one of the arms being connected
to the adjacent end of the tie situated on the corresponding side
of the pitch axis of the blade by connection means making a
secondary articulated connection, in such a manner that in the
relative initial position of the rigid members of each tie the
centers of the main balls connecting each tie to the two
corresponding blades and the center of the secondary articulated
connection of each tie to the corresponding arm of the members
making the connection to the two corresponding blades are
substantially aligned on the longitudinal axis of the tie.
5. A rotor head as claimed in claim 4, wherein the connection
member has the shape of a V open towards the hub, with the free end
of one of the arms in the form of a pivot clevis on the adjacent
end of a tie, the pivoting axis of the clevis on the end of the arm
being parallel to the lag axis of the corresponding blade.
6. A rotor head as claimed in claim 5, wherein a connection eye
fastened to one of the rigid members of a tie is engaged and
retained between the two branches of an end clevis of an arm of a
connection member, whose other arm has an end piece engaged in and
fastened to the two branches of a connection clevis fastened to at
least one other rigid member of a neighboring tie.
7. A rotor head as claimed in claim 6, wherein said connection eye
of a tie is retained in the end clevis of an arm of a connection
member by a secondary ball of laminated elastomer.
8. A rotor head as claimed in claim 1, where in the means for the
articulated connection of each of two neighboring ties on one and
the same blade comprise a respective one of two main balls disposed
on the corresponding connection member symmetrically, one on each
side of the pitch change axis of the blade, each of these balls
being connected to the tie situated on the same side of the pitch
change axis as the ball in question by means of a ball eye
surrounding the ball in question and separated from the other ball
eye only by a slight transverse clearance at right angles to the
pitch change axis of the blade.
9. A rotor head as claimed in claim 1, wherein the means for the
articulated connection of each of two neighboring ties on one and
the same blade comprise a respective one of two main balls disposed
on the corresponding connection member in positions radially offset
along the pitch change axis of the blade, each of these balls being
connected to a respective one of said neighboring ties by a ball
eye surrounding it.
10. A rotor head as claimed in claim 9, wherein said main balls are
radially offset along the pitch change axis of the blade and are
each centered on said axis.
11. A rotor head as claimed in claim 9, wherein the main ball
connecting one end of each tie to the member connecting a blade to
the hub is radially on the outside of the other main ball held on
the member connecting the blade to the hub, while the main ball
connecting the other end of the tie to the member connecting a
neighboring blade to the hub is radially on the inside of the other
main ball held on the member connecting the neighboring blade to
the hub.
12. A rotor head as claimed in claim 8, wherein at least one ball
eye held on a connection member, connecting a blade to the hub, by
one of the two corresponding main balls is directly fastened to at
least one of the two rigid members of the tie articulated on said
connection member by the corresponding main ball.
13. A rotor head as claimed in claim 8, wherein at least one ball
eye held on a member connecting a blade to the hub by one of the
two corresponding main balls has a connection arm fastened to at
least one rigid member of the tie connected to said connection
member by the corresponding main ball.
14. A rotor head as claimed in claim 1, wherein each tie comprises
an elongated central rigid plane plate engaged at least partially
between two external rigid plane plates, which are elongated in the
same direction and to each of which the central plate is connected
by a layer of a viscoelastic material bonded to the two plates
connected together by it, the central plate being provided with an
end piece having a pivot eye extending on one side, in the
direction of the elongated plates, beyond the outer plates, while
the latter have on the other side in the direction of the elongated
plates, and beyond the inner plate, a clevis for fastening by means
of at least two bolts to an end piece of an arm making the
connection to a main ball, each tie being mounted between two
blades in such a manner that the plane of the plates is
substantially parallel to the lag axes of the two blades.
15. A rotor head as claimed claim 1, wherein each member connecting
a blade to the hub carries, radially on the inside of each main
ball held by it, two feet projecting laterally relative to the
connection member and extending in the one case on one side and in
the other case on the other side of the pitch change axis of the
corresponding blade, each of these two lateral feet having a stop
surface facing the hub and intended to come to bear against one of
two lag stop surfaces which are directed towards the outside of the
hub and towards the end of the corresponding blade, and each of
which is provided on a respective one of two projecting bosses on
the outer radial face of the hub and laterally on each side of said
connection member and of the corresponding articulation means, in
order to limit the lag deflections of the blade on the starting and
stopping of the rotation of the rotor, through the direct bearing
of the stop surface of a lateral foot against a lag stop surface of
the hub.
16. A rotor head as claimed in claim 15, wherein one of the two
lateral feet of each connection member is extended laterally beyond
the corresponding stop surface and is shaped as a lever controlling
the pitch of the corresponding blade.
17. A rotor head as claimed in claim 1, wherein each member
connecting a blade to the hub is a radial clevis comprising an
upper branch and a lower branch, which are disposed facing one
another and are spaced apart in the direction of the lag axis of
the corresponding blade, and the outer radial ends of which are
integral with the corresponding blade root, which is forked, or
retain between them the root of the corresponding blade, while
their inner radial ends are fastened to an inner radial frame of
the means effecting the articulation on the hub, which means also
have an outer radial frame fixed on a part of the hub and disposed
between the two branches of the clevis, each of the corresponding
main balls being retained and substantially housed between the two
branches of the clevis, radially between their outer radial ends
and the outer radial frame, which is also disposed between
them.
18. A rotor head as claimed in claim 17, wherein each main ball is
on the one hand housed between two bosses projecting towards one
another on the face of a respective one of the branches of the
clevis which faces the other branch, and on the other hand is
retained by a diametrical pin whose axis is parallel to the lag
axis of the blade and which passes through the ball and the bosses
and is fixed on the two branches.
19. A rotor head as claimed in claim 8, wherein each member
connecting a blade to the hub is a radial clevis comprising an
upper branch and a lower branch, which are disposed facing one
another and are spaced apart in the direction of the lag axis of
the connecting blade, and the outer radial ends of which are
integral with the corresponding blade root, which is forked, or
retain between them the root of the corresponding blade, while
their inner radial ends are fastened to an inner radial frame of
the means effecting the articulation on the hub, which means also
have an outer radial frame fixed on a part of the hub and disposed
between the two branches of the clevis, each of the corresponding
main balls being retained and substantially housed between the two
branches of the clevis, radially between their outer radial ends
and the outer radial frame, which is also disposed between them and
wherein each main ball is housed in a part mounted as a brace
between the two branches of the clevis and having at least one ball
socket which opens laterally towards one side of the clevis and
towards the hub and in which a main ball is retained about a
diametrical axis at right angles to the lag axis of the blade and
substantially at right angles to the longitudinal axis of the tie
which this ball connects to the clevis.
20. A rotor head as claimed in claim 19, wherein each of the two
main balls is received and retained in a respective one of two
separate parts mounted as braces between the two branches of the
clevis.
21. A rotor head as claimed in claim 15, wherein each member
connecting a blade to the hub is a radial clevis comprising an
upper branch and a lower branch, which are disposed facing one
another and are spaced apart in the direction of the lag axis of
the corresponding blade, and the outer radial ends of which are
integral with the corresponding blade root, which is forked, or
retain between them the root of the corresponding blade, while
their inner radial ends are fastened to an inner radial frame of
the means effecting the articulation on the hub, which means also
have an outer radial frame fixed on a part of the hub and disposed
between the two branches of the clevis, each of the corresponding
main balls being retained and substantially housed between the two
branches of the clevis, radially between their outer radial ends
and the outer radial frame, which is also disposed between them and
wherein the two lateral feet provided with the stop surfaces, and
where applicable with the pitch control lever, are made as a single
piece, which is mounted as a brace between the branches of the
clevis, to which branches it is fixed in a radial position between
the main ball or balls and that part of the hub to which the outer
radial frame of the corresponding articulation means is fixed.
22. A rotor head as claimed in claim 1, which comprises a hub
provided with a rigid peripheral rim of circular or substantially
polygonal shape, the side or apices of which are rounded and which
is fixed for rotation with a rotor-mast unit about the axis of
rotation of the rotor, and wherein said articulation means of each
member connecting a blade to the hub are substantially housed
inside the rim and connect said connection member to a part of said
rim of the hub.
23. A rotor head as claimed in claim 22, which comprises an
integrated tubular hub-mast unit having said rim in its top portion
and being provided for each blade with at least one opening formed
in the hub-mast unit in a position substantially adjacent the rim,
while a part of the corresponding connection member passes through
said opening in order to connect the blade, outside the hub-mast
unit, to the corresponding articulation means, inside the hub-mast
unit.
24. A rotor head as claimed in claim 22, which is provided with a
top curved fairing covering the upper part of the hub and having
cavities for the passage of the means connecting the blades to the
hub, said fairing preferably being mounted floating on the ring of
ties and being connected by silentblocs at its periphery to arms
connecting ties to the corresponding main balls.
25. A rotor head as claimed in claim 1, which comprises a hub
having a substantially radial plate of substantially circular or
substantially polygonal shape, which has rounded sides or apices
and which is fixed for rotation with a rotor-mast unit about the
axis of rotation of the rotor, the plate having formed in it a
number of cavities equal to the number of blades, while the
articulation means of the member connecting a blade to the hub are
at least partially housed in the corresponding cavity and bear
against the outer radial edge of said cavity, being connected to
the blade by a top part and a bottom part of said connection
member, said parts extending respectively above and below the
plate.
26. A rotor head as claimed in claim 1, which comprises a hub
having two substantially radial plates fixed for rotation with a
rotor-mast unit about the axis of rotation of the rotor and spaced
apart in the direction of the axis of rotation of the rotor, so
that for each blade they have two outer radial plate parts facing
one another, between which are retained the articulation means of
the corresponding member making the connection to the hub, as well
as at least an inner radial part of said connection member.
Description
FIELD OF THE INVENTION
The present invention relates to rotors, particularly the rotors of
rotary-wing aerodynes whose articulated head is equipped with a
drag interblade connector device comprising resilient return ties
with built-in damping the number of the ties being equal to the
number of blades and each of them being installed between two
neighboring or adjacent blades or between the means connecting two
neighboring blades to the hub.
The invention relates more particularly to the main or lift rotors
of helicopters, whose head is provided with an interblade connector
device of the type defined above and each blade of which is
advantageously connected to the hub by connection and articulation
means advantageously comprising a single articulation for flapping,
lag and pitch.
In the best form of construction of the rotor head to which the
invention relates the single flapping, lag and pitch articulation
included in the means articulating each rotor blade to the hub is
advantageously one of the so-called "laminated spherical thrust
bearing" type comprising--between two frames rigidly connected to
the hub, in the one case, and, in the other case, to the root of
the blade or to a member, such as a clevis or a sleeve, connecting
the root of the blade to the hub--an alternating stack, in the form
of portions of a sphere, of rigid cups and sheets of an elastic
material which have a common center and simultaneously effect, on
the one hand the transmission to the hub of centrifugal forces
originating from the blade through the axial compression of the
laminated thrust bearing and, on the other hand, tho angular
flapping lag or drag and pitch movements of the blade relative to
the hub through the deformation of the elastic spherical sheets of
the laminated thrust bearing about their common center.
PRIOR ART
In order to damp the angular lag oscillations of the blades there
have been proposed numerous constructions of resilient-return
braces with built-in damping, of the viscoelastic, hydroelastic or
other type, which are sometimes called blade lag dampers or blade
lag frequency adaptors and which are interposed between the rim or
the peripheral edge of the rotor hub, to which each blade can be
connected by means comprising a single spherical elastomer
articulation for lag, flapping and pitch, and the blade root or a
member connecting the blade root to the hub, such as a sleeve or a
clevis. Examples of such braces are described in French Patent Nos.
2,528,382, 2,573,829 and 2,592,696.
In comparison with this well known type of mounting, in which the
resilient return and the damping of the angular lag movements of
each blade are effected simultaneously but independently of the
other blades because of the attachment to the hub of one end of the
two end articulations of the brace, whose other end articulation is
connected to the blade, the interblade arrangement of resilient
return ties with built-in damping is more advantageous in respect
of the general installation architecture, mass, dimensions,
parasitic lag of the rotor, and also in respect of reliability,
essentially because it makes it possible to eliminate from the hub
itself any attachment for the resilient return and the damping of
the driven blades.
The braces connecting the blades to the hub have in fact defects in
respect of reliability and strength, because they are stressed by
forces transmitted to them by short lever arms at the articulation
joints of each brace, so that these articulations are subjected to
substantial angular oscillations and forces. In addition, the
clevis fastening the brace to the hub must be fixed in a zone of
the hub which is the most critical, particularly when the hubs are
made of composite material, more especially integrated tubular mast
hubs. Furthermore, a problem of dimensions arises, which is linked
to problems of installation and dimensioning resulting from the
need to dispose not only the clevis for the attachment of the brace
on the hub but also a pitch control lever for the corresponding
blade, which must be disposed in the same zone. This also has the
consequence that the radius of the attachment of the blade by its
root on a sleeve or clevis making the connection to the hub is
large, especially if it is desired to fold back the blade. In a
general way the space available near the hub is too small to allow
the accommodation of braces or lag dampers, or else lag frequency
adaptors, which are very stiff and are subjected to considerable
forces and therefore have large dimensions and mass, giving rise at
the same time to a not negligible increase of the aerodynamic drag
of the entire rotor, not to mention the fact that the hydroelastic
damping braces, which make it possible to seek an acceptable
compromise between moderate stiffness and high damping, pose
specific problems of reliability and leaktightness where the
hydraulic damper is concerned.
It is for all these reasons that various interblade connection
devices utilizing resilient ties and in some cases with built-in
damping were proposed a long time ago, particularly in French
Patent Nos. 948,640, 1,465,027, 2,125,150 and in U.S. Pat. Nos.
2,494,985 and 3,302,726.
The use of resilient return interblade ties with built-in damping
makes it possible to regulate the natural frequencies and the lag
damping of the blades in relation to one another and not
individually in relation to the hub, thus opposing out-of-phase lag
oscillations of the blades without opposing in-phase lag
oscillations, which are free; this has the effect of displacing the
natural transmission modes and eliminating all damping for this
type of oscillations. Another effect of interblade connection
utilizing resilient return ties with built-in damping, where the
operation of the rotor head is concerned, is that the blades assume
a position of equilibrium in lag as if they were each connected to
the hub and freely articulated on the latter. For ground resonance
the first vibratory mode in lag is of influence only through the
rotational unbalance caused by the phase displacement of the blades
relative to each other, and not through their individual movement
relative to the hub.
This operating principle of an interblade connection device is
confirmed in French Patent No. 1 465 027 relating to a helicopter
rotor having a rigid hub and articulated blades. On this rotor each
blade makes its angular lag oscillations about a pivot parallel to
the axis of rotation of the hub and on the free end of a radial arm
of the rigid hub, and each blade is connected to each of the two
neighboring blades of the rotor by a tie or connection device
comprising resilient means and damping means. By one of its ends
each tie is articulated on a strap connecting a blade to the
corresponding radial arm of the hub, in a zone of said strap which
lies ahead of the pitch change axis of said blade, in relation to
the direction of rotation of the rotor. The other end of the tie is
also articulated on the blade connection strap of the blade
immediately preceding the corresponding arm of the hub, but in a
zone of said strap which is situated in rear of the pitch change
axis of said preceding blade. Each connection strap has a generally
triangular shape and is rigidly connected to the corresponding
blade by one side of the triangle and pivoted on the corresponding
radial arm of the hub by the apex opposite said side, while the
connection on strap is articulated by each of the other two apices
of the triangle on one of the two ties articulated to said strap,
so that the articulations on the ties are offset to the greatest
possible extent, taking into account the dimensions of the
connection strap, one of them towards the front and the other
towards the rear in relation to the pitch change axis of the
corresponding blade. In this way the articulations of the two ends
of a tie and the articulations on the hub of the two blades
connected together by said tie form a deformable articulated
quadrilateral, which is a parallelogram when the angular lag
oscillations of the blades are zero or in phase.
French Patent Ser. No. 948,640 describes a helicopter rotor in
which each blade is connected by its root to a blade support
mounted, for pivoting about a lag axis, on a radial member pivoted
on the rotor hub about a flapping axis situated radially inside the
lag axis, in relation to the center of the hub, and along the pitch
change axis of the blade, the root of which is coupled to a lever
controlling the pitch of the blade in question. Each blade support
carries two side legs which extend in the plane of rotation of the
blades and project radially outwards and, at the same time,
forwards for one leg and rearwards for the other leg in relation to
the pitch axis of the blade, relative to the direction of rotation
of the rotor, each of these legs being formed at its end as a ball
joint eye. Ties each extend between two neighbouring blades, to
each of which the corresponding tie is connected by a universal
joint, which articulates it on the side leg on the corresponding
side on the support of the corresponding blade. Each tie comprises
two tubes partially nested telescopically one in the other, the
free end of each of them carrying a ball held in the ball joint eye
of the side leg on the corresponding side, on the support of one of
the two blades connected to one another by said tie, and the two
tubes of the latter are each fastened to one of two straps, which
are radial relative to the common axis of the tubes and which are
spaced apart and have inserted between them at least one block,
sleeve or ring of elastic material, such as rubber. Each ball joint
permits limited universal movement between the tie and the blade
support which are articulated to one another by said ball joint,
and the rubber members are designed to absorb small periodic
displacements due to higher order harmonics of the vibratory
conditions of each blade, independently of the other blades, to
which these small displacements are not transmitted, while these
rubber members are compressed or stretched with an amplitude such
that movements of high amplitude of a blade are transmitted to the
next blade by a tie. In particular, the independent angular
oscillatory lag movements of each blade are absorbed by the elastic
members, which return the two telescopic tubes of each tie to their
starting position, while movements of high amplitude in lag are
transmitted positively from one blade to the next by the ties, and
are thus made simultaneously by all the blades. Similarly, the
angular flapping oscillations of low amplitude, made independently
by each blade, are absorbed by the elastic members, the absorption
capacity of which is exceeded by high amplitude flapping
transmitted from one blade to the other and giving rise to a
variation of the taper angle of the rotor. This Patent Ser. No. 948
640 provides for the replacement of the elastic members by
hydraulic means for the purpose of making the connection between
the telescopic tubes of each tie. However, in all cases the elastic
members or the hydraulic means are selected in such a manner as to
provide a high degree of damping and great resistance to movements,
so as to permit effective elimination or reduction of the
vibrations of one blade relative to another. In a rotor of this
kind no other damping is provided for the blades than that due to
the relative friction of the two parts pivoting in relation to each
other on the lag articulation and through the hysteresis of the
material of which the elastic members are made (this material thus
being a viscoelastic material), or by the hydraulic damping
means.
French Pat. No. 2,125,150 describes a rotor whose hub of plastic
material reinforced with high resistance fibers has, for the
support of each of the blades, a flexible arm reinforced with a
radial bundle of these fibers and provided, near the central part
of the hub, with a flattened cross-section (in the direction at
right angles to the axis of the hub) evolving into a circular
section at the free end of the arm, which terminates in a
substantially radial cylinder portion on which is fixed a
cylindrical sleeve serving as pivot for a bush fastened to the root
of the corresponding blade. In this way the flexible arm permits
the angular flapping and lag oscillations of the blade, and the
virtual lag axis of the blade, in the direction of the pitch change
axis and in relation to the center of the hub, is situated radially
on the outside of the virtual flapping axis of the blade, but
radially inside its incidence articulation, which is interposed
between the blade and the corresponding flexible arm of the hub and
consists of the bush and the sleeve enabling the blade to swivel
about its longitudinal pitch change axis. In the variant shown in
FIG. 5 of this French patent short-stroke lag dampers are provided,
each disposed between two neighbouring blades, on which the damper
is retained by its ends fixed to lugs on the sleeves of the two
blades. At its radially inner end each sleeve carries two lugs or
pairs of lugs projecting laterally relative to the pitch axis of
the blade, one of them being directed towards the front and the
other towards the rear of said pitch axis, referring to the
direction of rotation of the rotor, so that the connection of a lag
damper to a sleeve will be, in the radial direction, on the inside
of the pitch change articulation and on the outside of the virtual
flapping articulation, and substantially in the zone of the virtual
lag axis but considerably offset laterally relative to said virtual
lag axis.
U.S. Pat. No. 2,494,985 describes a lag damper device for the
blades of the rotor of a rotating-wing aircraft, the head of which
rotor is articulated. The hub has a central part supporting a
radial arm for each blade and the end of each arm is arranged as a
clevis in which a first pivot is mounted for swivelling about an
axis parallel to the axis of rotation of the hub. Each blade has a
blade root in the form of a cylindrical sleeve mounted for
swivelling, with the aid of bearings, about a second pivot, which
is radial and with which the sleeve forms the incidence change
articulation of the blade. This radial pivot is extended towards
the center of the rotor by a clevis mounted for pivoting about a
third pivot, whose axis is simultaneously at right angles to the
pitch change axis of the blade and to the axis of the first pivot.
This third or flapping pivot passes through a central core, which
in turn is mounted for pivoting with the first pivot between the
two branches of the end clevis of the corresponding hub arm, so
that the first pivot is the lag pivot, and the central core is
mounted as a universal joint on the lag and flapping pivots, whose
axes, at right angles to each other, intersect on the pitch axis of
the corresponding blade but radially on the inside of the pitch
change articulation. A V-shaped lever is rigidly connected by its
base to the lag pivot, and its two arms extend simultaneously
radially towards the corresponding blade (that is to say outwards
relative to the center of the hub) and laterally, one towards the
front and the other towards the rear of the pitch axis of the
blade, relative to the direction of rotation of the hub, so that
its arms pivot with the blade about the lag axis. An elongated lag
damper is mounted by two end clevises for pivoting about axes
parallel to the lag axes, on one side on the free end of the front
arm of the V-shaped lever connected to the lag pivot of one blade,
and on the other side on the free end of the rear arm of the
V-shaped lever connected to the lag pivot of the blade immediately
preceding in the direction of rotation of the rotor, so that only
axial loads are transmitted from the arms to the damper when the
two blades are subjected to out-of phase angular lag oscillations.
The lag damper is arranged to change length with damping when the
relative positions of the two blades connected by it are changed.
The lag damper is provided with an elongated central plate carrying
an end clevis and engaged between two elongated lateral plates
carrying friction linings applied against the opposite faces of the
central plate, and with two transversal spring mechanisms effecting
adjustable gripping or clamping of the central plate between the
friction linings of the two lateral plates, which form the other
end clevis, in order to brake any axial displacement of the central
plate relative to the two lateral plates. However, this damper
provides no resilient return of the two blades connected by it to a
relative initial position, and, because of the shape and the
mounting of the V-shaped levers fixed for rotation with the blades
about the corresponding lag pivots, a damper and the two lever arms
connecting it to two neighbouring blades form a deformable
quadrilateral, which is an articulated parallelogram when the
angular lag oscillations are zero or in phase, the effective
articulation of each damper on a blade being laterally offset to a
considerable extent from the pitch axis of the blade in question,
because it is situated at the free end of the corresponding arm of
the V-shaped lever and not at the pivot point of the lever on the
end clevis of the radial arm of the hub, as the V-shaped lever is
fastened to the blade in its angular lag deflections.
U.S. Pat. No. 3,302,726 describes an articulated rotor head having
blades connected in pairs by linear lag dampers provided with
friction members, this rotor head being equivalent to that
described in U.S. Pat. No. 2,494,985 analyzed above, except with
regard to the precise structure of each damper, which is provided
with resilient bands surrounding the members mounted to slide and
to rub against each other, so that the friction, and consequently
the damping, is increased when the amplitude of the relative lag
displacement of the two blades connected by it increases, because
of the deformation to which the resilient bands are then subjected;
said bands then additionally exert a certain return action, towards
their initial position, on the friction members. However, with
regard to the pivotal mounting of each end of each damper on the
free end of an arm of a V-shaped lever opening radially towards the
outside and fastened by its base to rotate with the blade about the
lag axis, which intersects the flapping axis on the pitch change
axis of the corresponding blade but radially on the inside of the
pitch change articulation, this rotor head is directly equivalent
to that of U.S. Pat. No. 2,494,985.
All these known solutions therefore propose the articulation of
each end of a tie or lag damper on an arm or support foot fastened
to the member which, in the lag articulation of a corresponding
blade, is driven with the blade in its angular lag oscillations, so
that it pivots with the blade about its lag axis, and in such a
manner that the center of the articulation of each end of the tie
or of the lag damper is considerably offset laterally from the
pitch change axis of that blade and lies radially on the outside of
the lag axis, so that the centers of the articulations of the two
ends of a tie or lag damper and the lag axes of the two blades
connected by said tie are at the four apices of a deformable
articulated quadrilateral. This has the consequence that the
articulations of the ends of each lag damper are not stressed by
the pitch change movements of the two corresponding blades, whose
pitch articulations are situated radially on the outside of the lag
axes. In addition, the rotor heads of U.S. Pat. Nos. 2,494,985 and
3,302,726 and of French Patent Ser. No. 948,640 are articulated and
are provided, for each blade, with flapping, lag and pitch
articulations made in the form of independent pivots disposed
between a rigid part of the hub and the blade attachment means, in
such a manner that in the two American patents the flapping and lag
articulations are at the same level, whereas the blade pitch
articulation is radially offset towards the interior in relation to
the center of the hub, whereas in the French Patent Ser. No.
948,640 the flapping articulation is radially offset on the inside
of the lag articulation, which in turn is radially offset on the
inside of the pitch articulation, which also corresponds to general
configuration found in the rotor head of French Pat. No. 2,125,150,
in which the flexible radial arms of the hub have virtual flapping
and lag articulations.
The consequence therefore is that in the last two patents mentioned
the attachment means of the ends of the ties or lag dampers are
also stressed by the flapping movements of the blades, thus
entailing an undesirable coupling of lag and flapping.
It is also important to note that the articulated rotor heads
provided for each blade with an actual lag articulation, formed
about a lag axis parallel to the axis of rotation of the rotor, and
equipped with interblade ties as proposed in the abovementioned
prior art documents, are rotor heads which no longer correspond to
the architecture of the rotors of advanced design fitted on modern
helicopters now on the market, particularly rotors which have
blades and/or hubs of composite material and in which the blades
are connected to the hub by articulations which themselves are
likewise essentially composite.
SUMMARY OF THE INVENTION
The problem underlying the invention is to overcome the
disadvantages indicated above, and the invention seeks to provide a
rotor head equipped with interblade ties and the mounting of which
enables each tie to be stressed only by the angular lag movements
of the blades relative to each other, these angular lag movements
being completely disconnected from the angular pitch and flapping
movements.
Another aim of the invention is to provide a rotor head in which
each interblade tie makes it possible to introduce not only damping
but also a powerful resilient return in the angular lag movements
of the blades in relation to each other. Finally, yet another aim
of the invention is to provide a mounting of the interblade ties
which is compatible with rotor heads of advanced design and of the
the type comprising for each blade a single thrust bearing
articulation transmitting to the hub the centrifugal forces and
shearing forces originating from the blades and giving, about a
single central point of the thrust bearing articulation, the three
degrees of freedom of the blade in respect of flapping, lag and
pitch, without the existence on the rotor head of a physical lag
axis about which the angular lag oscillations of a corresponding
blade are made, while the means directly connecting each blade to
said thrust bearing articulation, namely the blade root, which in
turn is in the form of a clevis or connection sleeve, or else an
independent member shaped as a clevis or connection sleeve,
undergoes combined angular flapping, lag and pitch movements.
To this end the object of the invention is a rotor head of known
type, comprising a hub to which each blade of the rotor is held by
a connection member fixed to the blade and connected to the hub
with the aid of articulation means permitting angular oscillations
of the blade about a single point on which the flapping axis, the
lag axis and the pitch change axis are convergent, the rotor head
also comprising an interblade connection device consisting of
elongated resilient-return ties with built-in damping, the number
of which ties is equal to that of the blades and which are mounted
substantially in a ring around the hub, so that each of them
connects together two neighboring blades of the rotor, each tie
comprising at least two rigid elongated members, each of which is
provided with means for the articulated connection of a respective
end of the tie to a respective one of the two blades connected by
said tie, and which are connected to one another by at least one
resilient-return member of the two rigid members, for return to a
relative initial position, and by at least one member damping all
relative movement of the two rigid members, at least in the
longitudinal direction of the tie, and according to the invention a
rotor head of this kind is characterized in that the means for the
articulated connection of each tie to a blade comprise a main ball
whose center is situated on or in immediate proximity to the
longitudinal pitch axis of the blade and which is retained, on the
means connecting the blade to the hub, radially on the outside,
relative to the center of the hub, of the point of intersection of
the lag, flapping and pitch change axes of the blade, which point
constitutes the single center of articulation of the means making
the connection to the hub. In this way the controlled oscillatory
movements of the blade about its pitch change axis give rise to no
parasitic stressing of the ties connected to it, and this is very
favorable in respect of their life and their dimensions because of
a reduction of weight and size.
At the same time it is advantageous that the means articulating the
connection member of a blade on the hub comprise a thrust bearing
articulation of the laminated spherical type constituting at one
and the same time a lag articulation a flapping articulation and a
pitch articulation, with its center al the intersection of the
flapping, lag and pitch axes of the corresponding blade, thus
providing the advantage of eliminating the principal parasitic
couplings on the rotor head.
In a first preferred embodiment the means for the articulated
connection of two neighboring ties on one and the same blade
comprise a single main ball whose center is situated on the pitch
change axis of the blade.
In this case it is advantageous for the single main ball to be
connected to the adjacent ends of the two neighboring ties by a
rigid connection member comprising two arms radially inclined
towards the hub and disposed laterally one on one side and the
other on the other side of the pitch change axis of the blade, the
two arms being attached to one another by a ball eye surrounding
the main ball, and the free end of one of the arms being connected
to the adjacent end of the tie situated on the corresponding side
of the pitch axis of the blade by connection means making a
secondary articulated connection, in such a manner that in the
relative initial position of the rigid members of each tie the
centers of the main balls connecting each tie to the two
corresponding blades and the center of the secondary articulated
connection of each tie to the corresponding arms of the members
making the connection to the two corresponding blades are
substantially aligned on the longitudinal axis of the tie, thus
enabling misalignment to be taken up.
It is advantageous for the connection member to have the shape of a
V open towards the hub, with the free end of one of the arms in the
form of a pivot clevis or pivot eye on the adjacent end of a tie,
the pivoting axis of the clevis or of the eye on the free end of an
arm being parallel to the axis of the main ball, which is likewise
substantially parallel to the lag axis of the blade, so as to
ensure good overall stability in compression, with the aid of
V-shaped connection members which are extremely easy and
inexpensive to produce.
In this case a connection eye fastened to one of the rigid members
of a tie may advantageously be engaged and held between the two
branches of an end clevis of an arm of a connection member.
In order to absorb small movements due to higher flapping harmonics
and to movements of the blades when the rotor is stopped, occurring
at the secondary articulated connection means, that is to say
between one end of a tie and the free end of a corresponding arm of
a member making the connection to a blade, the connection eye of a
tie is advantageously held in the end clevis of the arm of the
connection member by a ball of laminated elastomer material.
In a second preferred form of construction of the rotor head
according to the invention the articulated connection means of each
of two neighboring ties on one and the same blade comprise a
respective one of two main balls disposed on the corresponding
connection member symmetrically, one on each side of the pitch
change axis of the blade, each of these balls being connected to
the tie situated on the same side of the pitch change axis as the
ball in question by means of a ball eye surrounding the ball in
question and separated from the other ball eye only by slight
transverse clearance at right angles to the pitch change axis of
the blade.
As an alternative to this construction, in which each member
connecting a blade to the hub is connected to the two adjacent ties
by two identical balls as close to one another as possible, the
means for the articulated connection of each of two neighboring
ties on one and the same blade comprise a respective one of two
main balls disposed on the corresponding connection member in
positions radially offset along the pitch change axis of the blade,
on which axis each of the main balls is centered, each of these
balls being, in this case also, connected to a respective one of
the two neighboring ties in question by means of a ball eye
surrounding it.
In this variant, in which the two main balls are radially offset
along the pitch change axis of each blade in order to restore a
certain mounting symmetry and to re-balance the distribution of
stresses in the different ties despite the radially offset mounting
of two neighboring ties on one and the same blade, it is
advantageous for the main ball connecting one end of each tie to
the member connecting a blade to the hub to be radially on the
outside of the other main ball held on the member connecting the
blade to the hub, while the main ball connecting the other end of
the tie to the member connecting a neighboring blade to the hub is
radially on the inside of the other main ball held on the
connection member of the neighboring blade.
In the two configurations comprising, on each member connecting a
blade to the hub, two main balls, at least one ball eye held on
said connection member by one of its main balls is directly
fastened to at least one of the rigid members of the tie
articulated on said connection member by the corresponding main
ball. However, it is also possible for at least one ball eye, held
by one of the corresponding main balls on this member connecting a
blade to the hub, to have a connection arm articulated on at least
one rigid member of the tie connected to said connection member by
the corresponding main ball.
On each of the ties used at least one resilient return member may
consist of a return mass composed of an elastically deformable
material, and at least one damping means may be constructed in the
form of a hydraulic damper, so that each tie may have a structure
similar to that of the hydroelastic braces described in the
previously mentioned French patents and serving to connect each
blade to the hub, or else a structure similar to that of one of the
resilient return braces with built-in damping described in French
Patent No. 2,063,969 of the Assignee.
In particular, for reasons of simplicity of production,
reliability, size, mass, lag and cost, it is advantageous that in
the different preferred forms of construction of the rotor head
according to the invention each tie should, as indicated in claim 9
of French Patent No. 2,063,969, comprise an elongated central rigid
plane plate engaged at least partially between two external rigid
plane plates, which are elongated in the same direction and to each
of which the central plate is connected by a layer of a
viscoelastic material bonded to the two plates connected together
by it, in accordance with a known structure in which the
viscoelastic material is subjected to shearing stresses by relative
longitudinal displacements of the central plate and of the outer
plates, the central plate being in addition provided with an end
piece in the form of a pivot eye extending on one side, in the
direction of elongation of the plates, beyond the outer plates,
while the latter have on the other side, in the direction of the
elongation of the plates and beyond the central plate, a bolted
connection to the end of one of the arms of the rigid V-shaped
member articulating the main ball on the member connecting a blade
to the hub.
In addition, each tie is advantageously mounted between two blades
in such a manner that the plane of the plates is substantially
parallel to the lag axes of the two blades, a feature which, in
conjunction with the low mass of such ties when their rigid plates
are of light alloy, means that the effects of the centrifugal
forces to which such ties are subjected are negligible.
Furthermore, in order to limit in an absolute manner the lag
deflections of each blade, in one direction during the starting-up
phases of the rotor and in the other direction during the rotation
braking phases of the rotor, each member connecting a blade to the
hub advantageously supports, radially on the inside of each main
ball which it retains, two feet projecting laterall relative to the
connection member and extending in the one caseon one side and in
the other case on the other side of the pitch change axis of the
blade, each of these two lateral feet having a stop surface facing
the hub and intended to come to bear against one of two lag stop
surfaces which are directed towards the outside of the hub and
towards the end of the corresponding blade and each of which is
provided on a respective one of two projecting bosses on the outer
radial face of the hub and laterally on each side of the
corresponding connection member and of the means articulating the
latter on the hub. In this way the lag deflections of the blade on
the starting and on the stopping of the rotation of the rotor are
limited by the stop surface of a lateral foot which bears directly
against a lag stop surface of the hub.
In addition, one of the two lateral feet of each connection member
is advantageously extended laterally beyond the corresponding stop
surface and is shaped as a lever controlling the pitch of the
corresponding blade, so that this pitch control lever and one of
the direct lag stops carried by the blade are made in the form of a
single piece.
In order to facilitate the production of each member connecting a
blade to the hub and also the production of the articulation means
of this connection member and their cooperation, on the one hand,
with said connection member and, on the other hand, with the hub,
it is advantageous in the different forms of construction of a
rotor head according to the invention for each connection member to
be a radial clevis comprising an upper branch and a lower branch,
which are disposed facing one another and are spaced apart in the
direction of the lag axis of the corresponding blade and the outer
radial ends of which are integral with the blade root, which is
then forked, or retain between them the root of the corresponding
blade, while their inner radial ends are fastened to an inner
radial frame of the means effecting the articulation on the hub,
which means also have an outer radial frame fixed on a part of the
hub and disposed between the two branches of the clevis, each of
the corresponding main balls being retained and substantially
housed between the two branches of the clevis, between the outer
radial ends of said branches and the outer radial frame, which is
also disposed between them.
In this way it is possible for each main ball to be retained
directly about an axis parallel to the lag axis of the
corresponding blade and between the two branches of the
corresponding clevis. In particular, each main ball may, on the one
hand, be housed between two bosses projecting towards one another
on the face of a respective one of the branches of the clevis which
faces the other branch and, on the other hand, be retained by a
diametrical pin whose axis is parallel to the lag axis of the blade
and which passes through the ball and the bosses and is fixed on
the two branches of the clevis.
However, in the embodiments in which two main balls are retained on
each clevis connecting a blade to the hub, it is also possible for
each main ball to be housed in a part mounted as a brace between
the two branches of the clevis and having at least one ball socket
which opens laterally towards one side of the clevis and towards
the hub and in which a main ball is retained about a diametrical
axis at right angles to the lag axis of the corresponding blade and
substantially at right angles to the longitudinal axis of the tie
which this ball connects to the clevis.
In this last-mentioned case, it is possible to use a single part
mounted as a brace and having two ball sockets each receiving a
single ball, but it is likewise possible to mount two separate
parts between the two branches of the clevis, each part being
mounted as a brace between these two branches, while each of the
two main balls is received and retained in a respective one of
these two parts forming braces.
Furthermore, when the member connecting a blade to the hub is a
clevis, in order to facilitate its production as two separate
branches joined together, it is advantageous for the two lateral
feet provided with the stop surfaces, and where applicable with the
pitch control lever, to be made as a single piece, which is mounted
as a brace between the clevis branches, to which the brace thus
formed is fixed in a radial position between the corresponding main
ball or balls and that part of the hub to which the outer radial
frame of the corresponding articulation means is fixed.
Rotor heads according to the invention, as defined above, may be
produced by using hubs of different types the use of which has
recently been proposed for equipping modern helicopters.
In particular, the rotor head may have a hub of the type comprising
a rigid peripheral rim of substantially circular or substantially
polygonal shape, the number of sides and the number of apices being
equal to the number of blades and the side and/or apices being
rounded and the rigid peripheral rim being fixed for rotation with
a rotor-mast unit about the axis of rotation of the rotor, while
the articulation means of each member connecting a blade to the
hub, preferably a single laminated spherical thrust bearing, are
substantially housed inside the rim and connect the corresponding
connection member, preferably a clevis, to a part of the hub
rim.
The hub rim may be rigidly connected to a substantially
cylindrical, and optionally tubular, central member by which the
hub is fixed for rotation with the rotor-mast unit by means of
substantially radial spokes, which delimit, between the rim and the
central member of the hub, sockets in each of which may be mounted
the means articulating to the hub the member connecting a blade to
said hub.
However, the rotor head according to the invention advantageously
comprises an integrated tubular hub-mast unit having the rim in its
top portion and being provided for each blade with at least one
opening formed in the hub-mast unit in a position adjacent the rim,
while a part of the corresponding connection member passes through
said opening in order to connect the blade, outside the hub-mast
unit, to the corresponding articulation means housed inside the
hub-mast unit.
In order to reduce the overall aerodynamic drag of the rotor head,
particularly at the hub, it is then advantageous for the rotor head
to be provided with a top curved fairing covering the upper part of
the hub and having cavities for the passage of the members
connecting the blades to the hub, this fairing preferably being
mounted floating on the ring of ties and being connected by
silentblocs at its periphery to arms connecting certain ties to the
corresponding main balls.
However, it is likewise possible for the rotor head according to
the invention to comprise a hub of the type having a substantially
radial plate of substantially circular or substantially polygonal
shape, which has sides and/or apices which are likewise rounded and
which is fixed for rotation with a rotor-mast unit about the axis
of rotation of the rotor, the plate having formed in it a number of
cavities equal to the number of blades, while the articulation
means of the member connecting a blade to the hub are then at least
partially housed in the corresponding cavity and bear against the
outer radial side of said cavity, and are connected to the blade by
a top part and a bottom part of the connection member, said top-and
bottom parts extending respectively above and below the plate.
According to the invention it is also possible for the rotor head
to comprise a hub of the type having two substantially radial
plates fixed for rotation with a rotor-mast unit about the axis of
rotation of the rotor and spaced apart in the direction of the axis
of rotation of the rotor, so that for each blade they have two
outer radial plate parts facing one another, between which are
retained the articulation means of the corresponding member making
the connection to the hub, as well as at least an inner radial part
of this connection member.
In all of these known types of hub the invention will
advantageously be applied if the member connecting each blade to
the hub is a double radial clevis or a radial sleeve shaped as a
clevis at each of its radial ends, and has lateral openings to
permit the passage of the arms connecting the main balls to the
interblade ties, feet provided with the lag stop surfaces and a
pitch control lever being fixed on said sleeve, while the clevis or
the sleeve retains, at its outer radial end, the root of the
corresponding blade and the clevis or the sleeve is retained on the
hub by its inner radial end. Moreover, at the same time the means
articulating each connection member on the hub advantageously
consist of a single laminated spherical articulation, likewise
forming a thrust bearing, the inner radial frame of which
articulation is retained between the inner radial ends of the two
branches of the radial clevis or in the clevis of the inner radial
end of the connection sleeve, while the outer radial frame of the
laminated spherical thrust bearing is fixed against the hub rim or
against the inner radial edge of the cavity in the hub plate, or
else retained by at least one pin between two mutually facing parts
of the two plates of the hub, for example two superimposed radial
arms of the plates, depending on whether the hub is a rim hub, a
hub having a radial plate provided with cells or cavities, or
finally a hub having two superimposed radial plates.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and other advantages and
characteristics of the invention will emerge from the
non-limitative description given below of various examples of
embodiment which are described with reference to the accompanying
drawings, in which:
FIG. 1 is a partial plan view, partly in section through the plane
of rotation of the blades, of a rotor head having five blades and
of two of the five double clevises connecting the blades to the
hub, as well as of the resilient return interblade ties with
built-in damping which interconnect the clevises.
FIG. 2 is a view in section on the line II--II in FIG. 1 and shows
a double clevis connecting a blade to the hub, as well as its
connection and its articulation to the latter.
FIG. 3 is a similar view to FIG. 1, showing a second example of a
five-bladed rotor head, in which each of the blades is connected by
a double clevis, similar to that shown in FIG. 2, to the rim of an
integrated tubular hub-mast unit of the rotor.
FIG. 4 is a schematic view in half-section through a vertical,
substantially radial plane, on the line IV--IV in FIG. 3.
FIG. 5 is a similar view to FIG. 1, showing a third example of a
five-bladed rotor head.
FIG. 6 is a schematic view, partly in plan and partly in section in
the plane of rotation of the blades, of a fourth example of a rotor
head having four blades and a hub comprising a single radial plate
provided with cells or cavities for the connection of the blades to
the hub.
FIG. 7 is a partial view of a variant of the rotor head shown in
FIG. 6, wherein the mounting of the main balls connecting the ties
to each clevis connecting a blade to the hub has been modified.
FIG. 8 is a schematic view in section through a vertical,
substantially radial plane of the rotor head shown in FIG. 6, taken
on the line VIII--VIII in FIG. 6, and
FIG. 9 is a view similar to FIG. 8 in the case of a rotor head
whose hub comprises two radial plates spaced apart one above the
other.
DESCRIPTION OF THE PREFERRED EMBODIMENTS.
FIG. 1 shows part of a rotor head which has five blades and whose
rigid hub 1 comprises essentially a rigid rim 2 connected by five
substantially radial spokes 3 to a central cylindrical, tubular
body 4 which is fixed for rotation with a rotor-mast unit (not
shown) about the axis A of rotation of the rotor.
The rim 2, whose cross-section (through a vertical radial plane) is
substantially square (see FIG. 2), has in plan substantially the
shape of a regular pentagon whose sides and apices are slightly
rounded and convex, that is to say curved radially outwards
relative to the axis A, and the five spokes 3 are connected to the
rim 2 in the zones situated substantially in the middle of the five
sides of the pentagon. The spokes 3 thus delimit between them and
with the central body 4 and the rim 2 five cavities 5, in each of
which the means articulating a blade on the hub 1 can be
substantially housed, these articulation means bearing against the
inner radial face of the rim 2 at the rounded apex of the latter
which delimits the corresponding cavity.
The hub 1 may be entirely of metal or be made at least partially of
composite materials, in the latter case preferably with a
reinforcing strap or belt embedded in the rim 2.
The means articulating each blade on the hub 1 consist of a single
laminated spherical thrust bearing articulation 6 of a well known
type, comprising a central part 7 composed of an alternating stack
of rigid cups, generally of metal, and layers of elastomer in the
form of spherical domes, and bonded on the one hand against the
convex face of the spherical dome in an inner radial position on
the outer radial frame 8 of the thrust bearing 6, and on the other
hand against the concave face of the spherical dome in an outer
radial position on the inner radial frame 9 of said laminated
spherical thrust bearing 6.
As also shown in FIG. 2, the outer frame 8 is shaped as a bow
comprising an upper radial arm 8a and a lower radial arm 8b, with
the aid of which arms the outer frame 8 straddles the rim 2. In
addition, the outer frame 8 has a central, substantially radial
blind bore which leads out at its outer radial face between the
arms 8a and 8b and by which the outer frame 8 is positioned with
appropriate inclination relative to the rim 2 by means of a
cylindrical stud 10 inserted into said blind bore and projecting
radially inwards on the inner radial face of the rim 2. The outer
bow-shaped frame 8 is retained on the rim 2 with the aid of a strap
11 which is applied against the outer radial face of the rim 2 and
whose top and bottom ends project respectively above the top face
and below the bottom face of the rim 2 and are rigidly connected
respectively to the top arm 8a and the bottom arm 8b of the frame 8
by top and bottom threaded bolts 12 a and 12b respectively, whose
heads are held against the strap 11 and whose threaded stems are
screwed into the arms 8a and 8b respectively.
The inner frame 9 of the laminated spherical thrust bearing 6 is
mounted as a rigid brace between the inner radial ends of a top
plate 14a and a bottom plate 14b, which plates are joined together
to form the respective top and bottom branches of a double radial
clevis 13 making the connection to the corresponding blade. The
inner frame 9 is held between the branches 14a and 14b by two
threaded bolts 15 passing through coincident holes formed in the
frame 9 and in the branches 14a and 14b on axes parallel to the
axis of rotation A of the rotor and symmetrically one on each side
of the longitudinal pitch change axis X--X of the corresponding
blade, as well as by nuts 16 screwed onto the bolts 15. The two
branches 14a and 14b are disposed symmetrically to one another in
relation to the transverse plane at right angles to the axis of
rotation A of the rotor and passing through the pitch change axis
X--X of the corresponding blade; these branches 14a and 14b each
have the appearance of a radially elongated rigid plate having in
plan substantially the shape of an isosceles trapezium of very
great height. As shown in FIG. 2, the two plates 14a and 14b are
brought substantially closer to one another in their middle portion
and have outer radial ends 17a and 17b respectively which are
parallel and face one another, with sufficient spacing between them
in the vertical direction, parallel to the axis of rotation A of
the rotor, to receive and retain between them the root of the
corresponding blade with the aid of two pins (not shown), each of
which is held in two coincident holes 18 formed in the flat ends
17a and 17b on axes parallel to the axis A and symmetrically one on
each side of the corresponding pitch change axis X--X.
The radial clevis 13 is stiffened by another brace 19 mounted and
held rigidly by two bolts 20 between the branches 14a and 14b
connected together by said brace 19, which is disposed radially on
the outside of the rim 2, and the two bolts 20 likewise have their
axes parallel to the axis of rotation A of the rotor and are
symmetrical, one on each side of the pitch change axis X--X. On one
side of said axis X--X the brace 19 is extended by a lateral foot
21 extending in a direction inclined laterally towards the outside
of the clevs 13 and radially towards the rim 2, the free end of
which foot is provided, towards the rim 2, with a stop surface 22
substantially at right angles to the axis X--X. On the other side
of the axis X--X the brace 19 is also extended by a lateral foot
23, which likewise extends in a direction inclined laterally
towards the outside of the clevis 13 and radially towards the rim 2
and which likewise has, towards the rim 2, a stop surface 24
substantially at right angles to the axis X--X. However, the foot
23 is longer than the foot 21, and its portion extending beyond the
stop surface 24 is shaped as a pitch control lever, with an end
clevis 25 in which the top end of a pitch control connecting rod 26
is held by a ball joint.
For each blade the rim 2 has on its outer radial face two bosses
projecting outwards and situated laterally one on each side of the
corresponding clevis 13, each of these bosses carrying one of two
lag stop surfaces 27 and 28, which face towards the outside and
towards the end of the corresponding blade and are situated
respectively opposite the stop surfaces 22 and 24 on the brace 19.
In addition, the lag stop surfaces 27 and 28 are slightly curved
surfaces having a double curvature; they have a certain convexity
in a vertical plane parallel to that passing through the
corresponding axis X--X, and another slight convexity in the
horizontal plane passing through the same axis X--X, so that these
lag stop surfaces . 27 and 28 permit a certain pitch and flapping
movement while one or the other may be in contact respectively with
the stop surface 22 or 24, on the one hand when the rotation of the
rotor is started and on the other hand when this rotation is
stopped, because of the angular lag movements which are then made
by the corresponding blade about its lag axis, which is an axis
parallel to the axis A and passing through the center C of the
laminated spherical thrust bearing 6, that is to say through the
geometrical center of the spherical dome-shaped central portion 7
of said thrust bearing 6, this center C being in this example
situated geometrically on the pitch change axis X--X and in the rim
2, on its inner radial face side. It should be noted that the
flapping axis of the blade is likewise an axis at right angles to
the pitch axis X--X of the blade and passes through the center C of
the spherical thrust bearing, but this flapping axis is situated in
the plane of rotation of the rotor or lag plane of the blades.
Because of the articulation, on the rim 2, of each clevis 13
connecting a blade to the hub with the aid of a laminated spherical
thrust bearing 6, the angular flapping and lag oscillations of each
blade, and also the controlled changes of the angular orientation
of each blade about its pitch change axis through appropriate
action on the corresponding pitch control lever 23, are in fact
permitted by the shear deformations of the elastomer layers of the
laminated spherical dome-shaped part 7 of the corresponding
laminated thrust bearing 6, which transmits in compression in the
rim 2 of the hub 1 the centrifugal stresses and shear stresses
originating from the blade and transmitted to it by the plates 14a
and 14b of the clevis 13.
In a rotor head of this kind the stop surfaces 22, 24, 27 and 28
define a system of clean lag stops making it possible to limit in
an absolute manner the lag movements of the clevises 13 during the
rotor starting phases in one direction and the rotor braking phases
in the other direction, through the direct bearing of the clevises
13 against the hub rim 2.
The rotor head is also equipped with five resilient-return ties 29
with built-in damping (only three of them being visible in FIG. 1),
which each connect the clevises 13 of two neighboring blades of the
rotor and which serve as blade lag frequency adaptors in an
interblade connection device mounted in a ring around the hub 1.
Each tie 29 is an elongated member of a well known structure,
effecting resilient longitudinal return with powerful internal
damping due to plates of a viscoelastic material, which has high
deformation remanence, interposed between metal plates.
To be more precise, in this example each tie 29 comprises an
alternating stack of three elongated, substantially rectangular
plates of light alloy and two likewise substantially rectangular,
elongated layers of viscoelastic elastomer, so that in the central
position between the two outer plates 31 elongated in the same
direction, which is the longitudinal direction of the tie 29, the
elongated plate 30 is connected to each of them by a respective one
of the two elastomer layers 32, each of which is bonded by
vulcanization to the inner face of the corresponding outer plate 31
and to the oppositely situated face of the central plate 30. These
plates 30 and 31 and these layers 32 have a relatively slight
thickness in comparison with their length and width, so that the
tie 29 has the shape of a relatively flat member in which the
center planes of the plates 30 and 31 are parallel to one another.
The central plate 30 decreases in thickness from one end,
corresponding to a shorter side, towards its opposite shorter end
side, while each of the two outer plates 31 decreases in thickness
in the opposite direction, so that each elastomer layer 32 has a
substantially constant thickness. At its thicken end the central
plate 30 is extended beyond the thinner ends of the outer plates
31, to form an end portion 33 which is provided with an eye whose
axis is in the center plane of the central plate 30 and at right
angles to the longitudinal axis of the tie 29, while at their
thicker end each of the outer plates 31 is extended beyond the thin
end of the central plate 30 by one of the two parallel, spaced
branches of a connection clevis 34, coinciding holes being formed
in said branches. The end 33, which is provided with an eye, and
the clevis 34 constitute the two longitudinal ends by which each
tie 29 is connected to two neighboring clevises 13 by means of
connection members 35, each of which is in the form of a V-shaped
bent lever.
Each V-shaped lever 35 is rigid and comprises two arms 36 and 37
connected to one another at the base of the lever 35, which is
shaped as a ball joint eye 38, and the free end 39 of the arm 36
has holes formed in it to coincide with those formed in the clevis
34, so as to enable them to be fastened together by means of at
least two bolts, while the free end of the other arm 37 is in the
form of a clevis 40 for pivoting about an axis parallel to the axis
of the eye 38. Each lever 35 is mounted on a clevis 13 in such a
manner that its arms 36 and 37 are directed towards the hub 1 and
one on each side of the corresponding pitch change axis X--X, that
is to say in such a manner that each V-shaped lever opens towards
the hub 1 and its ball joint eye 38, directed towards the blade,
surrounds a ball 41 held in the clevis 13 by a diametrical pin 42
whose axis is parallel to the axes of the bolts 15 and at right
angles to the pitch change axis X--X, which it intersects at the
center of the ball 41, the pin 42 being retained by its head on the
top branch 14a and, on the bottom branch 14b, by a nut screwed onto
the threaded end of its stem, while the ball 41 is positioned
between two bosses 43 through which the pin 42 passes and which
project towards one another, one from the lower face of the top
branch 14a and the other from the upper face of the bottom branch
14b in order to secure the position of the center of the ball 41 on
the pitch change axis X--X of the corresponding blade. The end 33,
provided with an eye, of a tie 29 is articulated by a small ball 44
of laminated elastomer in the clevis 40 of the arm 37 of the
V-shaped lever 35. Thus, each clevis 13 connecting a blade to the
hub 1 is connected by a single main central ball 41, centered on
the pitch change axis of the blade in question, to the ring of
interblade ties 29, being for this purpose connected to two
neighboring ties of this ring by a corresponding V-shaped lever 35,
of which one arm 37 of the two arms 36 and 37 is connected by a
small secondary ball, such as 44, to the adjacent end of that one
of the two ties 29 which is situated on the same side of the pitch
change axis X--X of the blade as the corresponding arm 37 of the
lever 35. The axis of the eye 33 and of the clevis 40 is parallel
to the axes of the main balls 41, so as to ensure the overall
stability of the mounting of the ties 29 in compression, these ties
29 being mounted in such a manner that, at rest, the center planes
of their plates will be substantially vertical and parallel to the
axis A and that the center of the secondary articulation ball 44 of
one of the ends of each tie 29 and the centers of the two main
balls 41 connected together by said tie 29 will be in alignment on
the longitudinal axis of the tie 29. On the other hand, during
operation the small secondary balls 44 are intended to compensate
for misalignment.
This mounting of each tie 29 between two clevises 13 connecting two
neighboring blades to the hub has two effects on the operation of
the rotor head: the blades can assume a position of equilibrium in
lag, as in a rotor head on which they would be freely articulated,
the in-phase oscillations of the five blades being free, with the
consequence that the natural transmission modes are displaced and
all damping is eliminated for this type of oscillations. Thus, each
tie 29 is stressed only by out-of-phase or differential angular lag
movements of the blades relative to one another, with the
introduction of a powerful resilient return and a damping into
these out-of-phase angular lag movements, which are completely
disconnected from the angular pitch and flapping movements, so
that, in particular, the stresses on the interblade ties 29 give
rise to no annular pitch stresses on the clevises 13 and on the
pitch control associated with them.
During flight, under stabilized conditions, the known equality
between the cyclic pitch angle and the flapping of a blade, with a
phase displacement of 90.degree., has the consequence that the main
balls 41 connecting the ties 29 to the clevises 13 of the blades
undergo only cyclic movements of slight amplitude, so that the
plane described by the ties 29 in their rotation with the blades
about the axis A remains substantially parallel to the plane
described by the ends of the blades, if the small movements due to
the higher harmonics of the vibratory conditions are not taken into
account. With regard to the small secondary balls articulating the
ties 29 on the arms of the connection levers 35, these undergo only
small movements due to the higher flapping harmonics or to the
movements of the blades when the rotor is stopped. It will also be
noted that in this rotor head the only travel imposed on the ties
29 under static conditions originates from the small variations of
the distance between the axis A of the hub 1 and each tie 29, which
are due to the lag and the conicity of the rotor. Considered on the
axis of the ties 29, static travel of this kind would amount to
about 2 millimeters in the case of maximum flight, but in a rotor
head of a construction of this kind it is substantially eliminated
by the crushing of the compressed elastomer layers of the laminated
spherical thrust bearings 6 and by the radial deformation of the
rim 2 of the hub 1 through the action of cetrifugal force. A
preadjustment favorable to flight under full power is thus obtained
naturally. In addition, it is easy to adjust the stiffness of the
ties 29 according to requirements by adaptation of the mass of
viscoelastic material of the ties 29; damping will be adequately
ensured without exceeding the capabilities of known viscoelastic
elastomers. It is thus possible to obtain a rotor head which has no
coupling, and which has good ground resonance and air resonance
stability.
When the rotor is started up and when it is stopped, the lag stops
22, 24, 27 and 28 are loaded, if at all, only during a few
revolutions and with a low stress level, while permitting pitch and
flapping movements while the stop surfaces 22 are in contact with
the lag stop surfaces 27, or the stop surfaces 24 are in contact
with the stop surfaces 28. It may be noted that such a clean-acting
lag stop device cooperates advantageously with low flapping stops
of the type comprising a reciprocal ring mounted around the rotor
mast supporting the hub 1. Furthermore, because of the interblade
connections made by the ties 29, this rotor head eliminates the
risk of unbalance or shocks against the flapping or lag stops on
starting up, particularly when the helicopter is placed on a
sloping surface.
FIG. 3 shows a second example of a five-bladed rotor head, of which
each blade 45 is rigidly retained by its root 46 with the aid of
two pins 47 (one of which may be removable in order to enable the
blade 45 to be folded back by pivoting about the axis of the other
pin 47) between the outer radial ends of the top branch 14a and
bottom branch 14b of a double radial clevis 13, which has the same
construction and is mounted under the same conditions as in the
example illustrated in FIGS. 1 and 2. Thus, each clevis 13 connects
a blade 45 to the hub 51 with the aid of a laminated spherical
thrust bearing 6 of the kind described in the first example; the
outer and inner radial frames 8 and 9 respectively of said bearing
are respectively retained on the rim 52 of the hub 51 and disposed
as a brace between the branches 14a and 14b of the clevis 13 by
bolts 15, under the same conditions as in the first example.
Similarly, the clevis 13 has a second brace 19 carrying the lateral
feet 21 and 23 which are provided with lag stop surfaces and of
which one 23 is shaped as a pitch control lever. Finally, each
clevis 13 is connected, in the same way as in the first example, to
two neighboring ties 29 of an interblade connection device
comprising five resilient-return ties with built-in damping, which
are identical to the ties of the first example, by means of a
single main ball 41 centered on the pitch change axis X--X of the
blade 45 and held between the two bosses 43 inside the branches 14a
and 14b of the clevis 13 by a diametrical pin 42 whose axis is
vertical. The rim 52 of the hub likewise has the same shape in plan
and the same lag stops 27 and 28 as the rim 2 in the first
example.
However, in this second example the hub consists of the top part of
an integrated tubular hub-mast unit 51, the bottom part 53 of which
is directly driven rotationally about the axis A of the rotor by
the main transmission box of the helicopter, and which may be
constructed in accordance with the information given in the
Assignee's French Patent Nos. 2,584,995, 2,584,996 and 2,584,997,
the descriptions of which are incorporated in the present
specification by way of reference.
To be more precise, in this second example the rim 52 constitutes
the thickened top end of the integrated tubular hub-mast unit 52
made of composite materials and constructed in accordance with
French Patent No. 2,584,996, and therefore such that the hub-mast
unit 51 has formed in it a number of apertures 54 equal to the
number of blades and regularly distributed in the circumferential
direction over the periphery of the hubmast unit 51, in positions
adjacent the rim 52. The latter is in the form of a reinforcing
ring intended to take the centrifugal forces introduced into the
hubmast unit 51 by the laminated spherical thrust bearings 6, which
are substantially housed inside the hub-mast unit 51 and bear
against its inner face at the rim 52, being connected to the
clevises 13, the bottom branch 14b of each of which passes through
the corresponding opening 54 in the hub-mast unit 51, as
illustrated in the vertical half-section in FIG. 4.
In order to reduce the overall aerodynamic drag of the rotor head,
the hub-mast unit 51 is covered with a curved top fairing 55, which
in its peripheral part is provided with a number of openings 56
equal to the number of blades 45; these openings are so disposed
that each of them permits the passage of a clevis 13 with
sufficient clearance not to interfere with said clevis 13 in its
angular flapping, lag and pitch movements. The bottom part 57 of
the fairing, curved back towards the hub-mast unit 1, has an inner
radial edge sufficient by distant from the hub-mast unit 51 not to
interfere with the pitch control connecting rods connected to the
levers 23, or with the low flap stop device (not shown).
The fairing 55 may be rigidly fastened on the hub-mast unit 51 with
the aid of a cap (not shown) fixed on the rim 52 between the
clevises 13 and provided with a number of radial openings equal to
the number of blades; these openings are regularly distributed in
the circumferential direction on the cap, and each of them is
axially spaced from an opening 54 in the hub-mast unit 51 by the
rim 52, in order to enable the top branch 14a of the clevis 13,
whose bottom branch 14b passes through the corresponding opening
54, to pass through it.
However, in order to limit the size of the openings 56 in the
fairing 55 and to dispense with the support cap for said fairing,
the latter is advantageously mounted floating on the ring of ties
29, making use of the main balls 41 as support isolating the
fairing 55 from the pitch movements of the clevises 13, but driving
it in flapping movements and in the collective lag displacements.
As in the first example, each main central ball 41 is connected to
the two corresponding neighboring ties 29 by a connection member in
the form of a V-shaped lever, of which a clevis 40 at the end of
one arm 37 is connected by a secondary ball to the eye 33 on the
adjacent end of one of the two ties 29, while the end part 39 of
the other arm is rigidly connected by a bolted joint to the clevis
34 on the adjacent end of the other tie 29. Nevertheless, in order
to achieve the floating mounting of the fairing 55 on the rotor
head, only two V-shaped levers not adjoining one another are levers
35 identical to those in the first example, while the other three
V-shaped levers 35' have an arm 36' carrying at its end a connector
39 and having a substantially trapezoidal shape, widening from the
ball eye 38 (provided at the base of each V-shaped lever 35 or 35'
to surround the corresponding main ball 41) towards the end
connector 39 and radially outwards. At its apex directed radially
outwards, said arm 36' carries a small rubber block, in the form of
a silentbloc 58, on which the fairing 55 is fixed at the edge of
the corresponding cutout 56.
The three silentblocs 58, which attach the periphery of the fairing
55 to the three V-shaped levers 35', isolate the fairing 55 from
the differential lag movements of the blades, and the size of the
cutouts 56 can be reduced to the minimum necessary to allow the
passage of the clevises 13, their differential lag movements, and
the small movements due to the higher flapping-harmonics. The
rocking of the floating fairing 55, caused by the flapping of the
blades 45, is of an amplitude substantially equal to half that of
the flapping.
In addition to the advantages already mentioned in the case of the
first example, a construction of this kind is particularly
advantageous because of the great compactness of the integrated
hub-mast unit, and because the small radius of attachment of the
blades 45 (that is to say the short distance separating the pins 47
from the axis of rotation A of the rotor) permits a compact
fairing, so that the overall aerodynamic lag of the rotor head is
reduced. It will be noted furthermore that, in order to enable the
blades 45 to be folded back, only the bottom part 57 of the fairing
55 has to be eliminated or cut out appropriately.
It is clear that instead of an integrated tubular hub-mast unit
having one radial opening per blade and a rim at its top end, it is
possible to use an integrated tubular hub-mast unit having one pair
of radial openings per blade, these openings being situated one on
each side of a reinforcing belt. The top branch of the
corresponding connection clevis passes through one of them, and the
bottom branch of the same clevis passes through the other, as
described in French Patent No. 2,584,995. It is also possible to
use an integrated tubular hub-mast unit similar to that described
above with reference to FIGS. 3 and 4, but extended axially beyond
the rim 52 by an end portion having, for each blade, a cutout
opening into the free edge of said portion and corresponding
axially to the corresponding radial aperture in the hubmast unit,
so that the bottom and top branches of the corresponding connection
clevis pass respectively through the radial aperture and the
corresponding cutout in the hub-mast unit.
When the tubular hub-mast unit has a top end portion of this kind,
provided with cutouts, this portion may in addition, as also
mentioned in French Patent No. 2,584,996, be covered with a cap
fastened to the hub and also having for each blade a cutout opening
into its edge facing the rim, so that each cutout in the cap forms,
together with a cutout in the end portion of the hub-mast unit, a
top radial opening through which passes the top branch of the
corresponding connection clevis, the bottom branch of which passes
through the corresponding radial opening formed under the rim in
the hub-mast unit.
The five-bladed rotor head, of which part is illustrated in FIG. 5,
comprises an integrated tubular hub-mast unit identical to that
shown in FIGS. 3 and 4, with one radial opening 54 per blade 45 and
with a rim 52 at its top end, but the hub could be the one shown in
FIG. 1, with a rim connected by spokes to a central hub body.
Each blade 45 is connected to the rim 52 by a connection clevis
13', which differs structurally from the clevis 13 of the preceding
examples only in that between its top and bottom branches 14'a,
14'b it holds two main-balls 41a, 41b disposed symmetrically one on
each side of and in immediate proximity to the pitch change axis
X--X of the blade 45. Each main ball 41a or 41b is held by a
diametrical pin 42a or 42b fixed to the branches 14'a and 14'b, the
axis of this pin being parallel to the axes of the pins 47
connecting the root of the blade 45 to the clevis 13' and lying in
a plane at right angles to the axis X--X, in a radial position on
the inside of the pins 47 but on the outside of the brace 19
mounted between the branches 14'a and 14'b and just radially on the
outside of the rim 52; said brace carries lateral feet 21 and 23
provided with lag stop surfaces 22 and 24, the second of said feet
forming the pitch control lever. As in the preceding examples, each
clevis 13' is retained and articulated on the rim 52 by a laminated
spherical thrust bearing 6 the structure and mounting of which on
the rim 52 are in every way identical to the description given in
this regard with reference to FIGS. 1 and 2, so that the same
references are used in FIG. 5 to designate the same components,
without it being necessary to describe these components again.
In this example also the interblade connection device comprises
five resilient-return ties 29' with built-in damping, which are
mounted in a ring around the rim 52 and each of which is composed
of the same alternating stack of a central metal plate 30 and two
outer metal plates 31, together with two viscoelastic elastomer
layers 32, as in the first two examples. In addition, one
longitudinal end of each tie 29' consists of a bolted double
connection clevis 34, the two branches of which are formed by the
extensions of the two outer plates 31 beyond the inner plate 30. On
the other hand, the eyed end piece 33' fixed to the central plate
30 beyond the outer plates 31, and forming the other longitudinal
end of the tie 29' is an end piece whose eye 40' has its axis at
right angles to the center planes of the plates 30 and 31 and to
the axis of the clevis 34; said end piece is mounted directly
around the main ball 41a situated on the same side of the pitch
change axis X--X of a blade 45 as the tie 29' connected to said
blade on that side of the axis X--X and associated with said end
piece 33'. The clevis 34 of the other end of the tie 29' is
connected to the neighboring blade by an arm 36', of which one end
is in the form of a ball eye 38' directly surrounding the other
main ball 41b of said other blade. The other end of the connection
arm 36' is in the form of a small sleeve 39', the end of which is
engaged inside the two branches of the double clevis 34 and is
fixed to the latter by two bolts (not shown). The dimensions of the
main balls 41a and 41b and of each eye 38' or 40' are such that the
eye 40' is practically externally tangent to the eye 38' and is
separated from the latter only by slight transversal clearance in
the direction at right angles to the axis X--X.
The essential difference between this embodiment and the two
preceding examples is therefore that each clevis 13' connecting a
blade 45 to the hub is connected to each of the two ties 29'
adjacent to it by a respective one of two identical main balls 41a
and 41b held in the clevis 13' symmetrically one on each side of
the pitch change axis X--X of the corresponding blade, but as close
as possible to one another.
In comparison with the preceding examples, this configuration
introduces a collective blade pitch effect on the deformation of
the ties 29' in the absence of a differential lag of the blades,
but the arrangement of the main balls 41a and 41b as close as
possible limits this "static" deformation at extreme pitches to a
low value, of the order of 1.5 millimeter. On the other hand,
maintenance operations are facilitated, because each tie 29' can be
individually removed and replaced without it being necessary to
detach the two neighboring ties 29' from the corresponding clevises
13'.
Finally, in order to ensure that the main balls 41a and 41b will be
retained in each clevis 13' in such a manner that their center will
be in the plane of rotation of the rotor (a plane at right angles
to the axis of rotation A of the rotor and passing through the
pitch change axis X--X of the blade), these main balls are disposed
side by side between two internal bosses similar to the bosses 43
in FIG. 2, but extending transversely over the entire width of the
branches 14'a and 14'b of the clevis 13'. A bottom boss 43' of this
kind is shown schematically in FIG. 5.
The four-bladed rotor head shown schematically in FIGS. 6 and 8
comprises a hub 61 of a different type from those of the preceding
examples, since this is a hub having single plate 62 disposed
radially in relation to the axis of rotation A of the rotor and
fastened to a central tubular hub body 63 driven to rotate about
the axis A. The radial plate 62 is a substantially cruciform plate
in which the outer radial end of each of the arms is slightly
convex, while each arm is separated from a neighboring arm by a
concave cavity. In addition, the plate 62 has in each of its arms,
the number of which is equal to that of the blades, a cavity or
cell 65 formed through the plate 62 in a direction parallel to the
axis A and closed radially towards the outside by a rim 64 on the
plate 62. Each of the four blades (not shown) is connected to the
plate 62 of the hub 61 by a clevis 73 having two superimposed
radial branches spaced apart in the direction of the axis A; the
structure and arrangement of this clevis are substantially the same
as in the case of the clevis 13 in the first two examples. As also
shown in FIG. 8, the top and bottom branches 74a and 74b
respectively of the clevis 73 are held to one another and on the
plate 62, and at the same time articulated on the latter, by a
single laminated spherical thrust bearing 66, whose structure is
entirely similar to that of the laminated spherical thrust bearing
6 of the preceding examples; the alternating stack 67 of rigid
spherical domes and layers of elastomer works with compression and
shear of the elastomer between the outer radial frame 68, mounted
as a bow on the rim 64 of the corresponding cavity 65 and bolted to
said rim 64, and the inner radial frame 69 mounted as a brace
between the branches 74a and 74b, to which it is held by two
threaded bolts 75 cooperating with nuts 76. The whole arrangement
comprising the frame 69, the bolts 75, the laminated stack 67, and
the greater part of the inner frame 68 is substantially housed in
the corresponding cavity 65 in the plate 62. As in the first
example, the outer radial ends 77a and 77b of the branches 74a and
74b of the clevis 73 have formed in them two pairs of coaxial
apertures 78, facing one another, for the passage of pins
connecting the root of the corresponding blade to the clevis 73.
The two branches 74a and 74b of the latter are also held to one
another by a brace 79 mounted between these two branches radially
on the outside of the rim 64 of the corresponding cavity 65 in the
plate 62. This brace 79, which is held on the branches by bolts 80,
also has laterally projecting from it, on each side of the pitch
change axis X--X of the corresponding blade, feet 81 and 83 which
are curved towards the plate 62 and carry lag stop surfaces facing
lag stops 87 and 88 projecting from the outer radial face of the
corresponding arm of the plate 62. One 83 of the transversal feet
is extended to form a pitch control lever provided with a clevis 85
for connection to a pitch control connecting rod 86 lying
substantially in the concave cavity separating said arm from an
adjacent arm of the plate 62.
As in the preceding example, the hub 61 is surrounded by an
interblade device consisting of resilient return ties with built-in
damping, the number of which is equal to the number of blades and
which are mounted in a ring around the radial plate 62. In this
example, each of the four ties 89 is constructed very similarly to
the ties 29' shown in FIG. 5, since it comprises an alternating
stack of a rigid central plate 90 and rigid outer plates 91,
together with two layers 92 of viscoelastic elastomer, an eyed end
piece 93 extending the central plate 90 at one end of the tie 89,
and a connection clevis 94 extending the two outer plates 91 at the
other end of the tie 89. In addition, the mounting of each tie 89
on two neighboring clevises 73 each connecting blade to the hub is
similar to the mounting of a tie 29' in FIG. 5 on two neighboring
clevises 13', since a small connection sleeve 99 at one end of a
connection arm 96 is fastened to the end clevis 94 of the tie 89,
while a ball joint eye 98 provided at the other end of the
connection arm 96 is directly mounted around one 101a of the two
main balls 101a and 101b retained in the corresponding clevis 73,
and a ball joint eye 100 at the end of the end piece 93 is directly
mounted around the other 101b of the two main balls 101a and 101b
likewise retained in the other corresponding clevis 73. However, in
the example shown in FIGS. 6 and 8 the essential difference from
the preceding example is that the two main balls 101a and 101b, by
which each clevis 73 is connected to two adjacent ties 89, are
radially offset along the pitch change axis X--X of the
corresponding blade, while being separated from one another by the
shortest possible distance, taking into account the requirements
for the mechanical connection and clearances of surrounding
components, each of these two main balls 101a and 101b being
nevertheless centered on the pitch change axis X--X.
In FIGS. 6 and 8 each main central ball 101a and 101b is thus
retained in the corresponding clevis 73, as in the previous
examples, by a diametrical pin (not shown) whose axis is at right
angles to the plane of rotation of the rotor (that is to say to the
plane at right angles to the axis A and passing through the pitch
change axis X--X), and which passes not only through the
corresponding ball 101a or 101b but also through two bosses 103a or
103b which project from the branches 74a and 74b of the clevis 73
and which face one another towards the interior of the clevis 73.
The corresponding ball 101a or 101b is disposed between said bosses
in such a manner that its center is definitely on the pitch change
axis X--X of the corresponding blade under the same conditions as
the ball 41 lies between the bosses 43 in FIG. 2.
In addition, as shown in FIG. 6, each tie 89 is connected by the
ball joint eye 100 on its end piece 93 to the ball 101b in the
outer radial position on a connection clevis 73, and by the clevis
94 at its opposite end to the connection arm 96 connected to the
ball 101a in the inner radial position on the other clevis 73 to
which said tie 89 is connected.
In order to make possible this mounting of the balls 101a and 101b
on the clevises 73, and also their connection to the ties 89, it is
necessary for the axis of each ball joint eye 98 or 100 to be
parallel to the center plane of the corresponding tie 89 and to be
at right angles to the longitudinal axis of said tie 89, and
therefore the axis of the clevis 94 and of the small sleeve 99 must
be at right angles to the center plane of said tie 89.
Another possible mounting arrangement is illustrated schematically
as a variant in FIG. 7, in which once again it can be seen that
each clevis 113 connecting a blade to the hub is connected to two
adjacent ties 129 by two main central balls offset radially in
relation to each other along the pitch change axis X--X of the
corresponding blade, each of them being centered on said axis
X--X.
However, in this mounting arrangement the ball joint eye 140 at the
end of the end piece 133 extending the rigid central plate 130 of
each tie 129 is an eye whose axis is at right angles to the center
plane of the tie 129, while a double clevis 134 fastens the outer
rigid plates 131 at the other end of each tie 129 to the connection
arm 136 by means of bolts (not shown).
The ball joint eye 138 of the connection arm 136 surrounds a main
central ball 141a housed in a cavity 144a provided in a brace 143
fixed between the two branches 114a and 114b of the clevis 113,
while the ball joint eye 140 at the end of the end piece 133 of the
tie 129 directly surrounds the other main central ball 141b, which,
like the ball 141a, is centered on the axis X--X but is offset
radially on the outside of the ball 141a and also housed in a
cavity 144b provided in the brace 143. Each of the cavities 144a
and 144b forms a ball socket which opens laterally into a
respective one of the sides of the brace 143 and of the clevis 113,
being at the same time inclined radially towards the hub, in a
direction which corresponds to that of the longitudinal axis of the
corresponding tie 129 connected to the clevis 113 by the ball
housed in the socket in question. Each of the balls 141a and 141b
is retained in the corresponding socket 144a or 144b by a
diametrical pin passing through the socket and retained in the
opposite wall of the latter. The axis 142a or 142b of said pin is
on the one hand at right angles to the lag axis of the
corresponding blade, that is to say to the axis at right angles to
the plane of the rotor and passing through the center of the
laminated spherical thrust bearing, such as 66, which articulates
the clevis 113 on the hub, and on the other hand is substantially
at right angles to the longitudinal axis of the tie 129 connected
by the ball 141a or 141b in question to the clevis 113.
As a variant, the brace 143 bolted between the branches 114a and
114b of the clevis 113 may be replaced by two different braces,
each of which is also bolted between the branches 114a and 114b,
and may have only one of the sockets 144a and 144b to house the
sole corresponding ball 141a or 141b.
When each clevis connecting a blade to the hub is connected to each
of the two adjacent ties by a respective one of two main balls, it
is also possible, as a variant, for these two main balls to be, at
one and the same time, offset radially relative to one another
along the pitch change axis of the corresponding blade, and offset
laterally relative to each other, one on each side of said pitch
change axis. The two balls are then advantageously centered in the
plane of rotation of the rotor, symmetrically to one another in
relation to the point of intersection of the pitch change axis and
the axis passing through the centers of the two balls. In this case
both the radial spacing and the transverse spacing of the centers
of the balls must be as close as possible, while being compatible
with the mechanical members necessary for retaining the balls
between the branches of the corresponding connection clevis, and
also with the clearances of the mechanical members surrounding
these balls.
The mounting of an interblade connection device according to the
invention, in which the resilient-return ties with built-in damping
are connected, to the clevises connecting the blades to the hub,
with the aid of a single main ball or of two main balls retained in
each clevis and optionally centered on the pitch change axis of the
corresponding blade, is not limited to rotor heads whose hub is one
having a rim connected by spokes to a central hub body, or is one
having a rim supported by an integrated tubular hub-mast unit, or
one having a single circular or substantially polygonal radial
plate provided with cavities housing the means retaining and
articulating each clevis on the hub plate, as described for example
in French Patent No. 78,16,521 of the Assignee. The interblade
connection device according to the invention may in fact also be
used with and mounted on rotor heads whose hub comprises two
substantially radial plates disposed one above the other with
spacing in the direction of the axis of rotation of the rotor, and
having, for each rotor blade, two plate portions disposed facing
each other and holding between them the inner radial end of the
connection clevis and the means retaining and articulating said
clevis on the hub plates. Hubs of this type, having two radial
plates, are described for example in the Assignee's French Patent
No. 79,11,585, and the cooperation of a hub of this kind with a
connection clevis retaining a single main central ball for
connection to two adjacent interblade ties is schematically
illustrated in FIG. 9.
FIG. 9 shows once again a radial clevis 163 whose top and bottom
branches 164a and 164b respectively retain the root of the
corresponding blade between their outer radial ends 167a and 167b
with the aid of pins passing through mutually facing holes 168. The
two branches 164a and 164b are rigidly connected together in the
middle zone by the brace 169 fixed by bolts 170 and carrying feet
provided with lag stops and projecting laterally one on each side
of the clevis 163; in addition, one of said feet is in the form of
a pitch control lever. The two branches 164a and 164b are also
connected to one another at their inner radial ends by assemblies
comprising threaded bolts 165 and nuts 166, applying them on each
side against the brace formed by the inner radial frame 159 of a
laminated spherical thrust bearing 156. The outer radial frame 158
of the latter passes through cavities 171a and 171b formed
respectively in the top branch 164a and bottom branch 164b, in such
a manner that this outer radial frame 158 can be mounted as a brace
between radial arms 151 and 152 belonging respectively to a bottom
radial plate and an upper radial plate of the hub. The outer radial
frame 158 is held in position between the arms 151 and 152 of the
hub by bolts 153, 154; the center of the alternating stack 157 of
rigid cups and elastomer layers of the laminated spherical thrust
bearing 156 is situated in the plane passing through the axis of
the bolts 153. As in the example shown in FIGS. 1 and 2, a main
central ball 191 is retained between the internal bosses 193 of the
branches 164a and 164b of the clevis by means of a diametrical pin
(not shown), and this ball 191, centered on the pitch change axis
of the corresponding blade, is surrounded by a ball joint eye 188
on a connection member (V-shaped bent lever) at the adjacent ends
of two neighboring ties connected to clevis 163 under the same
conditions as in the example shown in FIGS. 1 and 2. In this
example the assembly comprising the inner radial end part of the
clevis 163 and the laminated spherical thrust bearing 156 is housed
between the mutually facing radial arms 151 and 152 of the hub
plates, and the cavities 171a and 171b of the branches of the
clevis 163 permit angular flapping, lag and pitch movements of the
clevis 163 with the corresponding blade about the center of the
laminated spherical thrust bearing 156, without any interference by
said clevis 163 with the brace-shaped outer radial frame 158 of
said laminated thrust bearing 156.
In all the embodiments of the invention each of the ties thus makes
it possible to introduce a powerful resilient return, as well as a
damping, into the angular lag movements of the blades relative to
one another, these angular out-of-phase lag movements being
completely disconnected from the angular pitch and flapping
movements, so that in particular the controlled pitch change
oscillations of the blades give rise to no stressing of the
interblade ties, and vice versa. Moreover, the interblade mounting
of the ties has several highly beneficial effects in respect of
forces taken and of resistance, since the lever arm is
substantially doubled, despite the compactness of the mounting
arrangement, in comparison with previous constructions, and this
results in the halving of the forces transmitted and the reduction
to one quarter of the rigidity required in the ties. In addition,
the balls and the ties are now subjected only to low static loads,
and the phase shift between the cyclic pitch and the flapping of
the blades eliminates a large part of the dynamic swiveling. The
absence of pitch-lag coupling eliminates loads induced by the ties
in pitch control and, in comparison with prior constructions
utilizing braces connected on the one hand to the blade root or to
the member connecting the blade to the hub, and on the other hand
to the hub, the number of connections permitting the introduction
of loads on the hub is reduced by half, whether the hub is
composite or metallic. Furthermore, holes and unevenness of shape
are eliminated in the most critical zones of the hub, since the
ties are not connected to the hub. This is of particular interest
when the hub is of composite material. Moreover, with regard to
each laminated spherical thrust bearing retaining and articulating
the clevis connecting a blade to the hub, the axial dynamic load
and the static lag load are eliminated, to the detriment of the
dynamic lag load, which is increased, although this increase is not
critical in comparison with the dynamic lag load found in modern
rotors having hubs of composite material. The vertical arrangement
of the ties having a plane overall shape, as well as their low
mass, has the consequence that the effects of the cetrifugal forces
to which they are subjected are negligible.
The mounting of the interblade ties is also very beneficial in
respect of reliability and maintenance, since the ties, being of
simple construction and easily capable of visual inspection, are
easily dismantled, which also applies to the balls connecting them
to the clevises; these balls have a long life because they are less
highly loaded and are subjected only to movements of low
amplitude.
Moreover, the mass of the rotor head can be reduced because of the
absence of a member connecting the ties to the hub, because of the
construction of the ties in light alloy and elastomer, because of
the short radius of attachment of the blades, and finally because
of the reduced eccentricity of flapping, particularly when the
rotor head comprises an integrated tubular hub-mast unit in which
the rim is relatively close to the axis of rotation of the rotor,
so that the distance between the lag and flapping axes and the
center of rotation of the rotor is short.
Substantially for the same reasons, the production cost of a rotor
head of this kind is reduced because of the absence of the member
connecting the ties to the hub and because of the very simple
technology for the production of the ties.
Although the radius of attachment of the blades can be reduced
because of the interblade mounting of the ties, it is possible for
the four or five blades of the rotors described above to be folded
back, provided that corresponding provision is made at the bottom
part of the top curved fairing of the rotor head, when such fairing
is fitted.
Because of the short radius of attachment of the blades, the
maximum cross-section of a five-bladed rotor head provided with
interblade ties remains relatively small, so that aerodynamic lag
is limited.
It will readily be understood that the mounting of the interblade
ties according to the invention is particularly interesting for a
rotor head having four or five or even more blades, particularly
when the blades are connected to a very compact integrated tubular
hubmast unit, preferably one of composite material.
* * * * *